The long-term goal of this research is to determine the neural basis of "choice" (behavioral hierarchies) and associative learning (classical and avoidance conditioning) on the synaptic level, using the marine gastropod Pleurobranchaea as an experimental preparation. Our work focusses on the feeding system of this mollusk, because the feeding behavior is intimately involved in both choice and learning. Specific objectives are: (1) to determine the neuronal mechanisms whereby feeding behavior "dominates" withdrawal behavior in Pleurobranchaea's behavioral hierarchy; (2) to study the neurohumoral mechanisms whereby egg laying dominates feeding in the behavioral hierarchy; (3) to analyze the neural basis of a demonstrated analog of classical conditioning in the isolated nervous system of Pleurobranchaea; (4) to perform behavioral experiments on a demonstrated form of avoidance learning in Pleurobranchaea, intended to determine the selectivity and retention time of this form of learning; (5) to continue neurophysiological and neuroanatomical studies of the neural circuitry controlling feeding, a project on which the first four aims depend. This work promises to provide the first cellular explanation of associative learning. Research on the egg laying hormone will further our understanding of how polypeptide hormones operate, perhaps providing insights into such polypeptide hormone disorders as diabetes. BIBLIOGRAPHIC REFERENCES: Kennedy, D. and Davis, W.J. 1977. The organization of invertebrate motor systems. In E.R. Kandel (Ed.), Handbook of Physiology, Vol. 2, Neurophysiology, Bethesda, Md.: American Physiological Society (in press). J. Comp. Physiol. A. 115, 1-27.